From Gene to Protein—Transcription and Translation
~Questions~
Introduction
1. What is a gene? State the definition, and give some examples of genes.
2. What is a protein? State the definition, and give some examples of proteins.
3. Complete the following table to summarize the basic characteristics of transcription and translation.
Original message or instructions in:
Molecule which Location where this
Is synthesized takes place
Transcription Nucleotide sequence in gene in DNA
in chromosome
Nucleus
Translation
4.
What is hemoglobin?
Transcription
5. Notice that the process of transcription is similar to the process of DNA replication. What are some
similarities between transcription and DNA replication?
6. There are also a few important differences between DNA replication and transcription. Fill in the
blanks in the following table to summarize these differences.
DNA replication
Transcription
The whole chromosome is replicated.
___________________is transcribed.
DNA is made.
DNA is double-stranded.
mRNA is made.
mRNA is _____________ -stranded.
DNA polymerase is the enzyme which
carries out DNA replication.
_____ polymerase is the enzyme which
carries out transcription.
T = thymine is used in DNA,
so A pairs with T in DNA.
T = thymine is replaced
by ___ = uracil in RNA,
so A in DNA pairs with ___ in mRNA.
7. After completing the transcription modeling procedure, summarize what you have learned by
explaining how a gene directs the synthesis of an mRNA molecule. Include in your explanation the
words and phrases: base-pairing rule, complementary nucleotides, cytoplasm, DNA, gene,
messenger RNA, nucleotide, nucleus, and RNA polymerase.
Translation
8. In the diagram below, circle the anti-codons in the tRNA molecules in the figure. Use arrows to
indicate where anti-codons in tRNA are matched with complementary codons in mRNA. To show
how the tRNA molecules would look after the correct amino acid has been attached, draw an asp
amino acid attached to the top left tRNA and a tyr amino acid attached to the top right tRNA.
(Figure 14.7 from Krogh, Biology, a
Guide to the Natural World, 2005)
9. Before following the translation modeling procedure, complete the table below that shows the codons
in your mRNA and the corresponding amino acids. Use the base-pairing rule to show the tRNA anticodon for each mRNA codon.
Amino acid
mRNA codon Anti-codon in tRNA molecule
that carries this amino acid
Threonine (Thr)
ACU
UGA
Histidine (His)
CAU
Proline (Pro)
CCU
Leucine (Leu)
CUG
Glutamic acid (Glu)
GAG
Valine (Val)
GUG
10. After step 5 in the translation modeling procedure, your model should look like this.
additional nucleotides…
What happened to the first tRNA? Why isn't it shown in this diagram?
Draw a rectangle around the third codon in the messenger RNA.
What is the anti-codon for that codon?
Which amino acid will be the third amino acid in the hemoglobin protein?
11. Describe one similarity in the structure of mRNA and tRNA.
12. What is the function of mRNA?
13. What is the function of tRNA?
14. The proteins in biological organisms include 20 different kinds of amino acids. What is the minimum
number of different types of tRNA molecules that must exist in the cell?
15. Explain why it makes sense to use the word translation to describe protein synthesis. (Hint: Look at
the figure on page 4 of your biology background and instructions handout.)
16. Explain why it would not make sense to use the word translation to describe mRNA synthesis.
17. What part of translation depends on the same base-pairing rule that is used in transcription and DNA
replication?
How the Gene for Sickle Cell Hemoglobin Results in Sickle Cell Anemia
18. In the table below, compare the DNA for the Beginning of the Normal Hemoglobin Gene
vs. the Beginning of the Sickle Cell Hemoglobin Gene.
What similarities do you observe?
What difference do you observe?
19. Complete the table. (Use the table on page 4 of your reading to help with translation.)
Beginning of Normal Hemoglobin Gene
CACGTAGACTGAGGACTC
Transcription produces:
codon
1
codon
2
codon
3
codon
4
codon
5
codon
6
amino
acid 1
amino
acid 2
amino
acid 3
amino
acid 4
amino
acid 5
amino
acid 6
Beginning of Normal Hemoglobin mRNA
Translation produces:
Beginning of Normal Hemoglobin Protein
Beginning of Sickle Cell Hemoglobin Gene
CACGTAGACTGAGGACAC
Transcription produces:
codon
1
codon
2
codon
3
codon
4
codon
5
codon
6
amino
acid 1
amino
acid 2
amino
acid 3
amino
acid 4
amino
acid 5
amino
acid 6
Beginning of Sickle Cell Hemoglobin mRNA
Translation produces:
Beginning of Sickle Cell Hemoglobin
Protein
21. What is the difference in the amino acid sequence of the hemoglobin molecules synthesized by
translating the sickle cell vs. normal hemoglobin mRNA molecules?
22. To summarize what you have learned, explain how a gene directs the synthesis of a protein. Include
in your explanation the words amino acid, anti-codon, codon, cytoplasm, DNA, mRNA, nucleotide,
nucleus, ribosome, RNA polymerase, tRNA, transcription, and translation. (Hint: You can use the
answer to question 8 on page 2 for the beginning of the answer to this question.)
23. Why does the cell need both mRNA and tRNA in order to synthesize a protein like hemoglobin?
24. Why does the cell need to carry out transcription before translation?
25. How does your DNA determine whether you develop sickle cell anemia?
26. Considering that we are all made up of the same 4 nucleotides in our DNA, the same 4 nucleotides
in our RNA, and the same 20 amino acids in our proteins, why are we so different from each other?